The long-term objective of the research is to further our understanding of the establishment and maintenance of pregnancy. We focus on the actions of signaling molecules originating in the placenta. Members of a family of proteins related to prolactin (PRL) are expressed in cell- and temporal- specific patterns in the uteroplacental compartment and have been shown to play a pivotal role in the establishment and maintenance of pregnancy. Prolactin-like protein-C variant (PLP-Cv) is new member of the family identified in recent years. It is expressed specifically in trophoblast giant cells and spongiotrophoblast cells of the rat placenta during the second half of gestation. Using an alkaline phosphatase (AP)-PLP-Cv fusion protein, we found that PLP-Cv exclusively bound to trophoblast giant cells and spongiotrophoblast cells within the junctional zone of the rat placenta. Thus, the same cells that produce PLP-Cv are also targets for PLP-Cv are also targets for PLP-Cv action. We hypothesize that PLP-Cv may be an autocrine/paracrine factor involved in the regulation of placental development/function. The Rcho-1 trophoblast cell lines has been proven to be a very useful model to investigate trophoblast cell development. We propose to utilize the Rcho-1 trophoblast cell line as an in vitro model to evaluate the effects of PLP-Cv on trophoblast cell proliferation and differentiation. We will also isolate the trophoblast cell receptor for PLP-Cv using an expression cloning strategy with the AP- PLP-Cv fusion protein as a probe. These findings will further our understanding of the intraplacental regulatory network involved in the control of placental development and maintenance of pregnancy.